In recent years, the Ethernet has been significantly developed in the field of industry control into a widely applied local area network technology, and an industry control network can intercommunicate with the global Internet conveniently by using the Ethernet. Moreover a large number of upper protocols have been applied successfully to the Ethernet technology, for example, the TCP/IP protocol has been applied successfully to the Ethernet technology, so the Ethernet can be applied conveniently in various applications.
A bus access scheme in the Time Triggered Architecture (TTA) is embodied as a Time Division Multiple Access (TDMA) scheme, where there are several timeslots included in one TDMA cycle. At most one of the timeslots in each cycle can be occupied by one switch, and the respective switches may transmit different data in each cycle.
With the Time Triggered Ethernet (TTE), a time trigger is made instead of an event trigger so that a communication task is transmitted based on a timing trigger by reasonable schedule to be temporally triggered for transmission to thereby ensure contention for a physical link in data transmission so as to guarantee real-time data transmission.
The TTE in the prior art can address the problem of contention for a physical link between devices to thereby guarantee real-time data transmission. Due to the TTE technology, although the problem of contention for a physical link between devices throughout the network can be solved, a considerable waste of bandwidth resources in the network may come therewith.
The following description will be given with reference to the drawings. FIG. 1 illustrates a schematic diagram of data transmission based on the TTE in the prior art. The network includes a plurality of Personal Computers (PCs) (nodes) including P1 to P4 respectively, and a plurality of switches including a switch 1, a switch 2, a switch 3 and a switch 4 respectively. Here data need to be transmitted in real time between the PC1 and the PC2, data need to be transmitted in real time between the PC2 and the PC3, and data need to be transmitted in real time between the PC3 and the PC4. In each scheduling cycle, a primary node allocates a timeslot to each of nodes so that in the timeslot allocated to the node, the entire physical link in a local area network, where the node is located, is for exclusive use by the node.
For example, data need to be transmitted in real time between the PC1 and the PC2, between the PC2 and the PC3, and between the PC3 and the PC4 through the switch 1 to the switch 2, the switch 2 to the switch 3, and the switch 3 to the switch 4 respectively. The primary node allocates timeslots to the PC1, the PC2 and the PC3 respectively in a temporally sequential order in each scheduling cycle. The PC1 transmits data through the physical link of the switch 1 to the switch 2 in the timeslot allocated thereto.
In the TTE mechanism, the same primary node can schedule only one node in one timeslot even if the physical links where the other nodes are currently located are not occupied. As no timeslots have been currently allocated to the other nodes, their physical links have to be idle. For example at this time the PC1 occupies the physical link of the switch 1 to the switch 2, and the entire physical link of the switch 1 to the switch 2 to the switch 3 to the switch 4 in the local area network where the PC1 is located is occupied by the PC1, so at this time even if the switch 2 to the switch 3, and the switch 3 to the switch 4 are idle, they may not be available to the other nodes, thus resulting in a considerable waste of network bandwidths, and the waste of network bandwidths will be exacerbated if there are a larger number of nodes in the physical link of the local area network.